I try to calculate the concentration of vapor benzene inside of the closed container. I first heated the container up to 100 oC to vaporize the liquid benzene (400 microliters). Then, I open a small hole with a needle and wait until the pressure equalizes with the atmosphere and connected it with my rector. My purpose is to give the known amount of gas into the reactor. Therefore, I give distilled water from another needle inside of this closed container to provide flow through the reactor with a 5 mL/min flowrate. I have to calculate the exact concentration of benzene entering the reactor. I need help with that calculation.
The Concentration and Vapour pressure have a relation you measure the vapour pressure and then calculate according to theoretical saturation concentration in the headspace above the liquid.
Ppm=VP in mm HG/760 mm HG X 106
Using the density of benzene, we can find the mass of benzene spilled, Density of benzene = 0.8 g/ml, MW of benzene = 78 mg/mmol, Since concentration = mass/(volume of air), Now we can calculate the concentration of benzene using the volume of air in the lab.
If I understand your experiment properly, you had a closed container with air and 0.4 ml of benzene in it at room temperature. This would be about 4.47x10^-3 mols of benzene. You then heated it to over 100 C but importantly I understand that all the benzene vaporized. You did not specify the size of the container, but if all the benzene vaporized and the container stayed sealed, the molar concentration of benzene in the container would be 4.47e-3/(4.47e-3+moles of air at room temperature in (volume of container-volume of liquid benzene)). Assuming that the benzene and air are well mixed and the temperature stays high enough that no benzene recondenses, this mole fraction will also be the concentration of benzene in the gas that you vented from the small hole and the concentration entering the reactor as you injected the water. Multiply the mole fraction by 10^6 to get it in (molar) ppm.
I just noticed that the container size is in the question heading but not in the details. 1 L of air at room temperature contains about 35.67 moles, so the concentration of the benzene was approximately 1.25 ppm.
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